The primary purpose of traffic barriers in bridge and highway construction is to constrain moving vehicles within their travel direction. Barriers are significant safety devices for the guidance (redirection) of a vehicle upon impact due to an accident or a vehicle malfunction. When such barriers are present on bridges and other roadway structures, the moving vehicles cannot be readily driven off the bridge and become airborne, nor can they cross over into oncoming traffic.
Construction of traffic barriers for use along the edge and atop the bridge or roadway surface may involve cast-in-place reinforced concrete or precast elements which are mechanically connected to their respective support such as, for example, a deck or a wall. However, both of these methods are labor-intensive and require the use of special forms and in most cases increase the period of time for construction due to the concrete curing requirements.
The safety significance of the bridge barrier has been recognized by the American Association of State, Highway and Transportation Officials (AASHTO) as evidenced by their 1989 publication entitled "GUIDE SPECIFICATIONS FOR BRIDGE RAILINGS", which are expected to become construction industry standards, possibly as early as 1993. These proposed specifications are, on average, much more demanding than existing standards in terms of the expected level of safety which must be capable of being provided by bridge railing and similar traffic barriers.
Basic traffic barriers separating two lanes of vehicular traffic are known in the art. U.S. Pat. No. 3,678,815 issued to Younker, for example, discloses a concrete traffic barrier which may be used in forming bridge guard rails, median barriers, and the like. The Younker barrier includes a pair of identically shaped shells which are bolted together leaving a void into which concrete is poured to form a core of solid material. U.S. Pat. No. 4,435,106 issued to Forster et al. discloses a traffic barrier which may be used to separate a roadway. The Forster traffic barrier may be cast-in-place through the use of forms to construct a solid concrete barrier which rises from the roadway edge outwardly first gently and then more strongly and then spaced below an overhanging guiding mechanism. A steep convex rise follows the gentle rise and transfers under the guiding mechanism into a flattened area.
Combining steel and concrete in a traffic barrier was disclosed in U.S. Pat. No. 4,496,264 issued to Casey. Casey discloses a barrier structure comprised of a number of spaced-apart, in-line vertical I-beam sections embedded in a roadway and having secured to the I-beams a number of form plates having a pair of downwardly and outwardly diverging pair of legs and a pair of upwardly diverging extending arms. Reinforcing rods are extended through aligned holes in the plates and side panels are connected to the panels. Concrete is poured down through the open top of the structure completely encasing the I-beams, panels, and reinforcing rods. The concrete bonds the side panels and a capping piece is pressed down into the concrete to form the steel and concrete traffic barrier.
Constructing concrete traffic barriers with precast concrete was first patented by Smith in U.S. Pat. No. 4,059,362. Smith discloses a highway traffic barrier composed of precast reinforced concrete barricades which are joined together. The alignment with each barricade is accomplished through the use of a horizontally and vertically tapered, vertical tongue-and-groove arrangement. This tongue-and-groove arrangement is molded onto the ends of each barricade with the wider portion of the taper at the bottom to facilitate the removal of one piece of the traffic barrier within an installation. The Smith barricade though is designed to be a highway median barricade and cannot be secured to a retaining wall.
A precast barrier design which can be used on retaining walls is disclosed in U.S. Pat. No. 4,494,892 issued to Wojciechowski. This design makes use of an interior channel of the barrier which directly contacts the top edge of the retaining wall. The projecting anchoring rods extend either transversely into a lateral precast concrete apron under the roadway surface or downwardly into the earthen support of the roadway. These projecting anchoring rods provide the support to withstand impacts from moving vehicles.
A method of construction in joining a precast concrete traffic barrier to a retaining wall is disclosed in U.S. Pat. No. 4,964,750 issued to House et al. This design provides for a profiled reinforced concrete block with a longitudinal channel void along its bottom surface. This barrier element will slide and rest on top of the retaining wall. U-shaped anchoring bars protrude from the precast barrier and the top of the retaining wall. A locking bar is inserted through the opening provided by the opposite U-shaped bars. Seating material is inserted through an opening in the barrier into the keyway, followed by grouting of the keyway.
Another known precast traffic barrier is U.S. Pat. No. 4,348,133 issued to Trent disclosing a precast polymer concrete shell which is placed at the construction site then filled with hydraulic concrete or other ballast through filling holes on top of the shell. However, the shell cannot be placed on a retaining wall since the shell must be entirely placed on the road or bridge surface.
A method of joining precast concrete barriers on substantially flat roadway surfaces is disclosed in U.S. Pat. No. 4,605,336 issued to Slaw. This design uses an upwardly projecting inverted U-shaped rod, which must be inserted into a narrow longitudinal channel, and a concrete reinforcing rod extending axially through the channel forms a longitudinal locking bar inserted to lock the barrier to the retaining wall. One problem with this design is that it can only be used on a substantially flat roadway and the alignment of the precast barrier and roadway must be precise to insure that the U-shaped rods are inserted into the rectangular inserts. Another limitation is a lack of tongue and groove connection to secure the barrier in place.
A serious drawback of conventional bridge or traffic barrier constructions is that their major structural material component, concrete, is heavy, costly and, absent substantial steel reinforcement, relatively limited in lateral impact resistance. And, as would be expected, the weight, cost and size of these predominantly concrete barriers increase as their specified minimum safety requirements also increase. Hence, as AASHTO and/or other municipal construction specifications for these barriers become increasingly demanding, so too will the costs of manufacturing, storing, handling and installing such barriers.
Therefore, the need for a traffic barrier able to meet increasingly demanding regulatory specifications and a more efficient method of manufacturing such a barrier is evident.